Projection display systems employing spatial light modulators require an exact direction of light so as to obtain a clear and undistorted image. Undesired light, such as light scattered by the components of the spatial light modulator, that reaches the display target of the display system will negatively effect the displayed image, distorting the object being viewed. An approach to solve this problem is to include a light-blocking device, such as a black mask or inactive area, inside the spatial light modulator.
Micromirrors are key components of microelectromechanical system (MEMS)—based spatial light modulators. A typical MEMS-based spatial light modulator usually comprises an array of miniature micromirrors. These micromirrors are selectively deflected, for example, in response to an electrostatic force, which in turn selectively reflect incident light to produce digital images. Therefore, undesired light can be prevented from reaching the target by turning the mirrors in the border areas to their inactive state. An inactive state is a state that is not associated with the image data of the image to be displayed in the display system. For this and other reasons, micromirror array devices, as well as other image engines such as liquid crystal devices or the like may include inactive areas in borders on all sides to avoid undesired light scattering.
In current spatial light modulators, the micromirror array devices are sealed within spaces between package covers and package substrates for protection purposes. The package covers either themselves are transmissive to the incident light, or comprise inlay windows that are transmissive to the incident light. In either configuration, the micromirror device array is aligned to the center of the package cover or the center of the inlay window of the package cover. In the presence of a light blocking mask, when the illumination light is incident at an angle to the surface of the micromirror array in the spatial light modulator, a group of micromirrors in the array will not be illuminated, and the modulated light from another group of micromirrors in the array will not be able to escape the package. As a result, the desired image will not be properly produced in the display target.